1680x1050 High Performance
At 1680x1050, the Radeon HD 5830 provided just 30fps while the GeForce GTS 450 was a fraction faster with 31fps. The Radeon HD 5850 and 5870 pumped 34fps and 37fps, while the GeForce GTX 460 managed 44fps. The GeForce GTX 470 was 2fps faster than its GF104-based sibling, but trailed the mighty GTX 480 by 3fps.
Again, it appears you'll require at least a mid-range graphics card from the present generation to enjoy Civilization V maxed at 1680x1050, and the GeForce GTX 460 is clearly the best choice at the moment.